Quantitative genetic aspects of embryonic mortality in White Leghorn chicken

Embryonic mortality of a long-term selected strain (PL2) with the objective of studying its quantitative genetic aspects were recorded through broken-open examination. The validity of two of the important assumptions involved in the estimation of genetic parameters i.e., normality of distribution and the relation between mean and standard deviation was examined. Embryonic mortality and its components depicted highly asymmetric distributions and a strong relationship between mean and standard deviation. Transformation of percentage observations to arcsine scales by two methods i.e., simple and Owen's method tended to decrease the magnitude of the non-normality but failed to change the significance of the various distribution statistics. Transformation slightly reduced the relation between mean and standard deviation but the correlation between mean and standard deviation continued to be significant (0.45±0.15 to 0.91±0.07). Heritabilities for total incubation mortality varied between 19.2±12.4 and 21.2±12.8% for different stages of mortality on percentage and arcsine scale. Heritability was high for late dead, pips and total mortality (12.8±11.2 to 21.2±12.8%) while it was low for early and mid-mortality (4.4±9.5 to 11.2±10.9%). There appeared a tendency for late-mortality to have as high heritability as that of total mortality. Adjustment of data for hatch effects had negligible effect on the heritability estimates. Transformation of data to the arcsine scale (simpleand Owen's method) did not lead to any consistent change in the heritability values.